Various arrangements have been disclosed for automatically guiding a vehicle along a predetermined path. Thus, in French Pat. No. 1 464 063 (Oleomat) there is disclosed a guiding device for a road working machine which is activated by means of a modulated electromagnetic beam. A similar device is disclosed in French Pat. No. 1 592 195 (Leon) in which there is described a road marking machine guided by means of an electromagnetic line of sight. In French Pat. No. 1 411 945 (Leningradsky Institute) a device is described for automatically guiding the machine for road works which machine is activated by a light beam or laser beam. In this case, the receptive device mounted on the guided machine is sensitive only to the guiding beam. These arrangements have proved to be impractical because of extraneous influences due mainly to sunlight interference.
In order to overcome these difficulties, it has been proposed to incorporate a "source" in the path of the machine which source emits radiation of a characteristic wavelength to which a receptive device on the guided vehicle is responsive. Thus, in U.S. Pat. No. 2 520 680 (Hamilton) there is described a seed-planter which automatically deposits a seed each time the planter passes over a previously deposited marker of a radioactive or suitably magnetised material. In U.S. Pat. No. 2 750 583 (McCullough) the vehicle is guided by means of a radioactive guideline defining the travel path of the vehicle, the guideline emitting radiation energy which is received by a radiation detector on the vehicle for adjusting the travel direction of the vehicle relative to the path.
In U.S. Pat. No. 3 229 660 (Lucas) there is disclosed apparatus for controlling the steering mechanism of a vehicle comprising a device for detecting signal elements previously applied to or embedded in the pavement along which the vehicle is intended to travel, the device being arranged to automatically activate the steering mechanism of the vehicle to adjust its direction of travel relative to the pavement. In this arrangement, the signal elements can be previously applied with paint and can be detected by means of a photo-electric device. In a further arrangement of this invention, there is disclosed the use of radioactive material embedded in the pavement in accordance with a predetermined pattern to be painted.
These arrangements suffer from the disadvantage that the location of a radioactive material in the path along which the vehicle is to be guided can be very costly. Furthermore, the radioactive material decays with time thereby losing its effectiveness in guiding the vehicle along the path. Lastly, these arrangements suffer from the serious disadvantage that they are continuously emitting radiation energy which may be undesirable from the point of view of safety and health.
Vrablik (U.S. Pat. Specification No. 3 298 352) describes an automated painting device for road markings provided with a scanner system which includes one or more signal-emitting sources and a guidance system which is automatically activated by signals from a receiving device capable of detecting the waves which, after emission from the source, are reflected by the road surface. This invention suffers from the disadvantage that the scanners are liable to pick up interfering waves which originate from other sources and are reflected off the road to the scanner.
It is an object of the present invention to provide an effective method of and apparatus for guiding an object relative to a predetermined path.